Dehydrogenation process and catalyst

ABSTRACT

MAGNESIUM CHROMITES PROMOTED WITH ALUMINUM HAVE BEEN FOUND TO BE SUPERIOR TO CHROMIA-ALUMINA TYPE DEHYDROGENATION CATALYSTS, FOR EXAMPLE, IN THE DEHYDROGENATION OF N-BUTANE. THE ALUMINUM IS EITHER ADDED TO THE PREFORMED MAGNESIUM CHROMITE OR IS INCORPORATED INTO THE SPINEL STRUCTURE OF THE CHROMITE ITSELF OR ADDED IN BOTH WAYS. THE ALUMINUM WILL BE PRESENT IN THE CATALYST FROM ALL SOURCES IN AN ATOMIC RATIO OF AL:CR OF 0.0004 TO 1.2:1. THE ATOMIC RATIO WILL MORE USUALLY BE 0.04 TO 0.8:1, AL:CR.

United States Patent 3,781,376 DEHYDROGENATION PROCESS AND CATALYSTHarold E. Manning, Houston, Tex., assignor to Petro- Tex ChemicalCorporation, Houston, Tex. No Drawing. Filed June 30, 1971, Ser. No.158,531

Int. Cl. C07c 3/28, 11/12 U.S. Cl. 260-6833 Claims ABSTRACT OF THEDISCLOSURE Magnesium chromites promoted with aluminum have been found tobe superior to chromia-alumina type dehydrogenation catalysts, forexample, in the dehydrogenation of n-butane. The aluminum is eitheradded to the preformed magnesium chromite or is incorporated into thespinel structure of the chromite itself or added in both ways. Thealuminum will be present in the catalyst from all sources in an atomicratio of AlzCr of 0.0004 to 1.2: 1. The atomic ratio will more usuallybe 0.04 to 08:1, AlzCr.

.other dehydrogenation cycle and so on.

The chromia-alumina catalysts have been recognized for a number ofyearsas the most preferred catalyst for this type of process. Thechromia-alumina catalysts are prepared by treating activated aluminawith a solution of chromic acid, draining oif the excess acid from thealumina, drying and heat treating at about 1400 F. Commercialchromia-alumina dehydrogenation catalysts normally contain about 20%chromium oxide. Preparative methods are shown, for example, in U.S.Pats. 2,399,678 and 2,419,997.

Other chromia-metal oxide materials have been investigated for theirdehydrogenation capabilities. One of the more prominent among these hasbeen chromia-magnesia which has been found to be a poor second tochromia-alumina. Several patents were issued to Tropsch in the late1930s relating to magnesia based chromia dehydrogenation catalysts,e.g., 2,122,786; 2,122,787; 2,122,- 790; and 2,148,140. Pitzer disclosedchromia-magnesiaalumina dehydrogenation catalyst in U.S. Pat. 2,638,455.

It is an object of the present invention to find an alternative catalystto chromia-alumina for use in cyclic dehydrogenation processes. It isanother object of the present invention to find a catalyst superior tothe chromiaalumina catalysts for use in dehydrogenation. It is still afurther object to provide a process which will give better results thanpresently achieved with chromia-alumina ice catalysts. Other objects andadvantages of the present invention will be apparent from the followingdescription.

DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS The objects ofthe present invention have been achieved by use of a novel catalystcontaining chromium, magnesium, aluminum and oxygen. The catalysts arecharacterized as magnesium chromites either in admixture with aluminumoxide or containing aluminum therein and can be considered as aluminumpromoted magnesium chromites. The chromites generally have a spinelstructure. This can be attributed to the octahedral site preferenceenergy of Cr which is the greatest of all cations which can formspinel-type structures. The crystal structure of the chromites willusually be a face centered cubic form.

The catalysts of the present invention are predominately chromites, thatis, they contain more than 50% by weight of the chromite. Preferably thecatalysts contain or more chromites, i.e., chromites. The chromitesgenerally may be represented by the formula MeCr O Where Me as statedabove is Mg, however, a portion of the magnesium can be replaced withother metals having an ionic radius approximately between about 0.5 and1.1 A., preferably between about 0.6 and 1.0 A. In the case of suchmixed chromites, Mg will be the predominant Me ion, comprising at least50 atomic per cent of the Me ions present. In addition to Mg the Me maybe one or more of the divalent ions of Ca, Sr, Ba, Fe, Mn, Co, Ni, Cu,Zn, or Cd.

The aluminum component of the catalyst may also be present as aconstituent of the chromite, however, it is not necessary that thealuminum be a portion of the chromite and may be present in addition tothe metal chromite in the form of aluminum oxide. The aluminum can beincorporated into the chromite by backing out a portion of the chromium.Aluminum can be substituted for up to less than 50% of the chromiumatoms of the chromite. Such chromites have the formula MeAl Cr ,,O whereMe has the designation previously given and x is a number of from morethan 0 up to less than 1.

The magnesium chromites of the present invention exhibit a certain typeof X-ray diffraction pattern. The peaks observed in the X-raydiffraction pattern may not have sharp peaks such as those found, e.g.,in highly crystalline material of the same chemical composition, but canand do frequently exhibit relatively broad reflection peaks. The degreeof sharpness of the reflection peak may be measured by the reflectionpeak band width at half height (w./h./2). In other words, the width ofthe reflection peak as measured at one-half of the distance to the topof the peak is the band width at half height. The band width at halfheight is measured in units of 2 theta. Techniques for measuring theband widths are discussed, e.g., in Chapter 9 of Klug and Alexander,X-Ray Diffraction Procedures, John Wiley and Son, N.Y., 1954. Theobserved band widths at half height of the preferred compositions ofthis invention are at least 0.12 2 theta and normally will be at least0.16 2 theta. The particular reflection peak used to measure the bandwidth at onehalf height is the reflection peak having Miller (hkl.)indices of 111. (See, e.g., Chapter of Klug and Alexander, ibid.). Thisdescription is not to be taken as a limitation of the invention inregard to the relationship between composition activity and band width.

Suitable catalyst according to this invention are magnesium chromitehaving X-ray diffraction peaks within the d-spacings 4.80-4.82,2.94-2.96, 2.50-2.52, 2.40-2.42, 2.07-2.09, 1.90-1.92, 1.69-1.71,1.59-1.61, 1.46-1.48, 1.40-1.42 and the most intense peaks being between250- 252.

Chromite formation can be accomplished by reacting an active compound ofchromium with an active compound of magnesium and the other designatedmetals. By active compound is meant a compound which is reactive underthe conditions to form the chromite. Starting compounds of chromium,magnesium or the other metals may be such as the nitrates, hydroxides,hydrates, oxalates, carbonates, acetates, formates, halides, oxides,etc.

The catalyst may contain an excess of chromium over the stoichiometricamount, which is 2 atoms of chromium per atom of Me(MeCr O There may befrom to 200 percent excess of the chromium. Similarly the Me portion ofthe chromite may be present in more than a stoichiometric amount.

The magnesium chromite can be prepared by precipitation, dry or wetmilling or mixing, by precipitation of one of the ingredients in thepresence of the other, coprecipitation and impregnation of one or moreof the solid ingredients with aqueous or non-aqueous solutions of saltsof the ingredients.

One particularly useful method of preparing the magnesium chromites hasbeen by coprecipitation from an aqueous solution. Soluble metal salts ofchromium, magnesium and any other metal component as described above aredissolved in water and an insoluble precipitate formed by the use of aprecipitating agent.

Soluble metal salts are known for essentially all metals. In specificregard to the metal components of the present invention the followingsoluble metal compounds are illustrative: chromium (III)nitrate,magnesium chloride, calcium sulfate, strontium tetrasulfidetetrahydrate, barium trisulfide, iron (II) nitrate, manganese (H)dithionate, cobalt (H) acetate, nickel nitrate, copper nitrate, zincsulfate, cadmium sulfate and aluminum sulfate. The precipitating agentin any compound which when reacted with the metal ion portion of thecatalyst forms an insoluble compound which can be converted to thechromite. The alkali and alkaline earth hydroxides such as NaOH, KOH,CaOH, as well as ammonium hydroxide cause the precipitation of the metalhydroxides which are converted on heating to the chromites. After theprecipitate is washed and dried it is calcined to form the chromite.

The formation of the chromite is obtained by heating the precipitates orother intimate mixture of chromite precursors at an elevatedtemperature, e.g., 400-1100 C. (generally no greater than 1300 C.), in acontrolled atmosphere, i.e., air, nitrogen, helium, a reducingatmosphere such as hydrogen, carbon monoxide or the like, for

The powder diffraction patterns may be made, e.g., with a Norelcoconstant potential diffraction unit type No. 12215/0, equipped with awide range goniometer type No. 42273/0, copper tube type No. 32147,proportional counter type No. 57250/ 1; all coupled to the Norelcocircuit panel type No. 12206/53. The copper K alpha radiation issupplied by operating the tube at a. constant potential of 40 kilovoltsand a current of 35 milliamperes. A nickel filter is used to remove Kbeta radiation. The detector voltage is 1660 volts and the pulse heightanalyzer is set to accept pulses with amplitudes between 10 and 30 voltsonly. Slits used are divergence 1, receiving .006 inches and scatter 1.Strip chart recordings for identification are made with a scanning speedof 1 per minute, time constant of 1 second and a full scale at 10 countsper second. No correction is made for K alpha, doublet or instrumentalbroadening of the band Widths.

a suflicient time, i.e., usually 5 minutes to 4 hours. A calcinationtemperature of 550-800 C. has been found particularly useful andtemperatures in the range of 600- 750 C. have been found to produceexcellent catalysts. Catalysts prepared at 900-1100" C. have also beenfound to be highly desirable.

The aluminum component of the catalyst as stated above can be addedprior to and/or after the calcination and formation of the chromite. Thealuminum component is conveniently added to the chromite as a solublesalt in a slurry with the chromite after which it is dried thendecomposed by heating to aluminum oxide. Alternatively insolublealuminum oxide can be added to the magnesium chromite, preferably in ahighly divided state. Yet another desirable way to place the aluminum inthe catalyst is by coprecipitation of aluminum hydroxide with the Mehydroxide and chromium hydroxide.

The aluminum will be present in the catalyst in all forms in an atomicratio of AlzCr of 0.0004 to 1.2: 1. For example, in terms of a solublealuminum compound such as aluminum sulfate, added to the magnesiumchromite this would represent from about 0.1 to 75 weight percent Al (SO16H 0 based on the total Weight of the catalyst. A more preferred rangeof AlzCr atom ratio is .04 to 0.8:1. Generally the higher weightpercentages of aluminum compound, i.e., 50 weight percent or more, areapplied to the magnesium chromites having high surface areas, e.g., 50m? per gram or more.

The active catalysts can be pelleted or applied to a suitable support,such as alumina, silica gel, silica-alurnina, firebrick, kieselguhr,quartz and the like. The catalyst is the active surface available forcontact with the gaseous reactants.

The catalysts of this invention can be applied to the dehydrogenation ofa wide variety of organic compounds. Such compounds normally willcontain from 2 to 20 carbon atoms, at least one grouping, having aboiling point below about 350 C., and may contain other elements, inaddition to carbon and hydrogen such as oxygen, halogens, nitrogen andsulfur. Preferred are compounds having 2 to 12 carbon atoms, andespecially preferred are compounds of 3 to 5 carbon atoms.

Representative materials which are dehydrogenated by the novel processof this invention include n-butane, ethyl toluene, alkyl chlorobenzenes,ethyl naphthalene, isobutyronitrile, propyl chloride, isobutyl chloride,ethyl fluoride, ethyl bromide, n-pentyl iodide, ethyl dichloride, 1,3-dichlorobutane, 1,4 dichlorobutane, the chlorofluoroethanes, methylpentane, methylethyl ketone, diethyl ketone, n-butyl alcohol, methylpropionate, and the like.

Among the types of organic compounds which may be dehydrogenated bymeans of the process of this invention are nitriles, amines, alkylhalides, ethers, esters, aldehydes, ketones, alcohols, acids, alkylaromatic compounds, alkyl heterocyclic compounds, cycloalkanes, alkanes,alkenes and the like.

Suitable dehydrogenation reactions are the following: acyclic compoundshaving 4 to 5 non-quaternary contiguous carbon atoms to thecorresponding olefins, diolefins or acetylenes having the same number ofcarbon atoms; aliphatic hydrocarbons having 6 to 16 carbon atoms and atleast one quaternary carbon atom to aromatic compounds, such as2,4,4-trimethylpentene-1 to a mixture of xylenes; acyclic compoundshaving 6 to 16 carbon atoms and no quaternary carbon atoms to aromaticcompounds such as n-hexenes to benzene; cycloparaflins and cycloolefinshaving 5 to 8 carbon atoms to the corresponding olefin, diolefin oraromatic compound, e.g., cyclohexane to cyclohexene or cyclohexadiene orbenzene; aromatic compounds having 8 to 12 carbon atoms including one ortwo alkyl side chains of 2 to 3 carbon atoms to the correspondingaromatic with unsaturated side chain such as ethyl benzene to styrene.

Illustration of dehydrogenations include butane to butenes and butadienepropionitrile to acrylonitrile; propionaldehyde to acrolein; ethylchloride to vinyl chloride; methyl isobutyrate to methyl methacrylate; 2or 3-chlorobutene-1 or 2,3-dichlorobutane to chloroprene; ethyl pyridineto vinyl pyridine; ethylbenzene to styrene; isopropylbenzene to a-methylstyrene; ethylchlorohexane to styrene; cyclohexane to benzene; ethane toethylene to acetylene; propane to propylene or methyl acetylene, allene,or benzene; isobutane to isobutylene; n-butane to butene andbutadiene-1,3; n-butene to butadiene-1,3 and vinyl acetylene; methylbutene to isoprene; cyclopentane to cyclopentene andcyclopentadiene-1,3; n-octane to ethyl benzene and ortho-xylene; monomethylheptanes to xylenes; ethyl acetate to vinyl acetate;2,4,4-trimethylpentane to xylenes; and the like.

The preferred compounds to be dehydrogenated are hydrocarbons with aparticularly preferred class being acyclic non-quaternary hydrocarbonshaving 3 to 5 carbon atoms or ethyl benzene and the preferred productsare propene, n-butene-l or 2, butadiene-1,3, vinyl acetylene, 2methyl-l-butene, 3-methyl-l-butene, 3-methyl-2- butene, isoprene,styrene or mixtures thereof. Especially preferred as feed are n-butene-lor 2 and the methyl butenes and mixtures thereof such as hydrocarbonmixtures containing these compounds in at least 50 mol percent.

The dehydrogenation reaction may be carried out at atmospheric pressure,superatmospheric pressure or at subatmospheric pressure. The totalpressure of the system will normally be about atmospheric pressure orsub-atmospheric pressure. Generally the total pressure will be betweenabout 1 p.s.i.a. and about 75 p.s.i.a. Preferably the total pressurewill be less than about 50 p.s.i.a.

The temperature of the dehydrogenation reaction will generally be in arange of about 350 to 700 C. with excellent results being obtained inthe range of 400 to 650 C. The gaseous reactant-s can be conductedthrough the reaction chamber at a fairly wide range of flow rates. Theoptimum flow rates will be dependent upon such variables as thetemperature of reaction, pressure, particle size of the catalyst, and soforth. Desirable flow rates may be established by one skilled in theart. Generally the flow rates will be within the range of about 0.10 to10 liquid volumes of the organic compound to be dehydrogenated pervolume of dehydrogenation zone containing catalyst per hour (referred toas LHSV). Usually the LHSV will be between 0.15 and about 5. Forcalculation, the volume of a fixed bed dehydrogenation zone containingcatalyst is that original void volume of reactor space containing catalst.

Ihe dehydrogenation is carried out in a series of cycles which comprisedehydrogenation of a suitable feed over the catalysts of the inventionunder the conditions as defined for a period of time, usually about 6 to'12 minutes followed by a regeneration cycle during which the cokedeposited from the dehydrogenation is burnt off. The regeneration can belonger or shorter than the dehydrogenation cycle as needed to remove thecoke, usually about 6 to 12 minutes will be sufficient. The coke isremoved by passing oxygen at a temperature of 550 to 650 C. over thecatalyst. A convenient source of oxygen is air, however, pure oxygen ora mixture of oxygen with inert gases, such as nitrogen, either in thesame or different proportions as air, can be used.

The following examples which are submitted to demonstrate the operationof the invention are divided into into two sections relative to thereactor. In the first example section the process was carried out zitatmospheric pressure, i.e., about 15 p.s.i.a. In the second section thereactions were carried out under vacuum. The absolute number of theresults vary as a result of the diiferent conditions, however, thetrends, results and relative difierences in catalysts types arecomparable. The presence of the chromite structure was established forthe catalysts by X-ray analysis as described previously. In the examplespercents are by weight except that results are given as mole percents.Analysis of the products was by gasliquid chromatography.

Example 1 The coprecipitated catalysts were prepared by the same method.In each instance CrCl .6I-I O and MgCr 6H O (in some cases AlCl .6 H O)were dissolved in demineralized water with about 1.4% dextran 2 toproduce an atom ratio of Mg/Cr of 1/2 unless specified otherwise. Thissolution was then added to concentrated NH OH, the precipitate filtered,washed and dried at 160 C. then passed through an 80 mesh screen andcalcined for 1 hour at the indicated temperature in air (unlessspecified otherwise) .and run through a hammer mill. The soluble salts,e.g.,

Al (SO .l6H O, were added by dissolving the salt in water, forming aslurry with the chromite (or in some cases the comparative commercialcatalyst) and heating the slurry to dryness in a mechanical tumbler toobtain even distribtuion of the soluble salts. The same procedure wasused to deposit the actives on a support.

Isothermal atmospheric reactor (Examples 2-23) The reactor was a 29 xinch Vycor tube equipped with a heating mantle and appropriateequipment. A 40 cc. bed of catalyst was placed in the reactor andreactant feed (or regenerative air) added at the bottom of the reactorwith product coming off overhead. The catalyst was heated to thereaction temperature in a nitrogen atmosphere. The process was carriedout automatically with a make cycle (dehydrogenation) of 9 minutes and 9minutes oxygen regeneration and repeat of the cycle. This gave a totalcycle time of 18 minutes. When desired, the partial pressure of then-butane during the reaction cycle was reduced below atmospheric bydilution with nitrogen. The total efliuent from either or both cycleswas collected in an inflatable collecting device and analyzed by gaschromatography. Alternatively, the efiluent from the regeneration cyclewas passed through a calibrated infrared analyzer to determine theamount of CO produced during regeneration (coke burn-off). By eithermethod of analysis the amount of coke deposited on a catalyst during thereaction cycle was determined and could be taken into account whencalculating the overall activity and selectivity of a catalyst. Thetemperatures were controlled by a thermoelectric temperature controllerand recorded on a Leeds and Northrup 24-point recorder.

EXAMPLES 2-11 These examples demonstrate the improvement accomplishedaccording to the present invention. The feed was 99 mole percentn-butane. The conditions and results are set out in Table I.

2 Dextran is a polysaccharide of 200,000-300,000 M.wt. and improves theprocessubility of the precipitate.

TABLE I Conditions:

LHSV=1.0 Tm=-600 0. Reaction cycle=9 minutes reaction/9 minutesregeneration Results, mole percent Partial Total pressue hrs. S Y

11- on Example Catalyst (atm.) stream C Bu Bd Bu Bd 2 Harshaw 7 Cr0211,%2" diameter pellets 1. 24 69 65 45 4 0. 33 26 67 69 10 46 7 a Houdry 10, $4" extrusions 1. 0 24 11 64 s 4 7 0.33 26 79 65 16 50. 5 l3 4 a"pellets of MgCrgOa l. 0 24 44 54 8.5 24 6 0. 33 26 38 48 16 18 45...;-..' /32 pellets of MgCrzO; plus 26 wt. percent 1.0 24 57 67 0 38 5AMSOOa-IBHaO 0. 33 26 56 66 37 48 6 96a" pellets, MgClzOq plus 20%Ah(SO)a- 1. 0 24 58 66 8 38 5 181120. 0. 33 26 55 63 15 8 7 MgCi'zO4 1 41.0 24 51 64 8 33 4 0. 33 28 46 61 15 28 7 8 MgCnOi l a 4 plus 0.012 molAl;(SO|)3-18HgO-.- 1. 0 24 59 66 8 39 5 0. 33 26 57 63 14 36 8 9 MgCIzOH4 plus 0.024 mole Al:(SO);-18H|O-. l. 0 24 64 69 8 47 5 0. 33 26 66 6814 44 9 1o MgCn04 1 plus 0.037 mole Al:(SO4)a'18H|O.. 1. o 24 66 68 s 455 0.33 26 68 67 15 46 10 11 MgCrzO; 1 1 4 plus 0.012 11101113304 1. 0 2452 62 8 32 4 l Coprecipitate of Cr/Mg 2/1 calcined at 600 C. for 1 hourin air. 9 Catalysts are 6-8 mesh particles of -55% actives deposited on7-9 mesh, HCl leached AMC alumina. 8 PP of n-C4=l.0 atm.=pure helm feed;pp of n-C4=0.33 atm.=hcbn plus N; diluent. 4 66.7 gills. of MgCrgO4. 0=conversion S =selectivity; Y=yield; Bu=butenes; Bd=butadlene. IUncalcined coprecipitate Cr/Mg=2/1 plus 20% Ah(SO4)a-18H:O then calcinedat 600 C. for 2 hours in air. 7 The Harshaw Chemical 00., Cleveland,Ohio. I Houdry Products and Chemical 00., Phiiadephie, Pa.

Examples 2 and 3 are two commercial catalysts employed in cyclicprocesses for dehydrogenation of butane. 45 'Examples 12 and 13 Examples4 and 5 are MgCrO which was pelleted and 6 through 10 are 55% activesdeposited on a fused alumina These examples show the improvementobtained with support. Example 11 was to determine if the sulfate wasaluminum salts other than the sulfate using 99 mole of any benefit. Bycomparison of Examples 11 and 7 it can percent butane as the feed. Theconditions and results be seen that the sulfate is of no benefit. 50 areset out in Table II.

TABLE II Conditions:

LSHV=LOTm-=600 0.

Reaction cycle=9 minutes reaction/9 minutes regeneration.

Results, mole percent Partial pressure 5 Y of 11-04 Example Catalyst 1(atm.) C Bu Bd Bu Bd 12 42.5 gms. MgCrzO4 plus 0.044 mole of Al(CH3COCH-1.0 58 67 9 39 5 COCHa)a. 0. 33 52 61 17 32 9 13 42.5 gms. of MgCrzOaplus 0.044 mole of Al(N0 91110.. 1. 0 62 8 43 5 0. 33 61 68 15 41 9 1Supported on 7-9 mesh AMC alumina. 1 PP of n-C4=1.0 atm.=pure hcbn feed;pp of u-C4=0.33 atm. =hcbn plus N1. Coprecipitated, calcined at 600 0.for 2 hours in air and run through a hammer mill.

Examples 14-19 The catalysts were prepared in the same manner as inThese examples demonstrate the efiect of the calcination 5:2 3:2 1th .ig i m the i i temperature of the MgCr O on the process results. Tablefor 2 601.91 T ys 5 cme a III shows the conditions and results. ours anammer m1 6 TABLE III LHSV=1.0 Tm=-600 C. Reactior1t)cyc1e=9 minutesreaction/9 minutes regeneration approx. 24 hours on stream for each runFeed=n-Butane (99 mole percen Results Partial pressure of n-Ci Catalyst(atm.) 2 O Bu Bd Bu Bd =2/1 calcined to 550 C; 42.5 grns. oi calcinedproduct plus 0.022 mole of Al2(SO4)3.18HzO.

prec. of Cr/Mg=2/1 calcined to 600 0.; 42.5 gms. of calcined productplus 0.022 mole of A12(SO4)3.18H2O.

16 Coprec. of Cr/Mg=2/1 calcined to 650 0.; 42.5 gms. of calcinedproduct plus 1. 0 68 0.022 mole 0fA12(S04)3-18H20- 0. 33 67. 5

a... of Cr/Mg 1.

Conditions:

Example 14 Coprec. of Cr/Mg 17 Co =2/1 calcined to 700 C.; 42.6 gms. ofcalcined product plus 0.022 mole of A12(SO4)3.18HO.

18 Coprec. of CrlMg=2/1 calcined to 750 0.; 42.5 gms. of calcinedproduct plus MgA1 C1' 4 Example 22 The catalyts in this case wasprepared by depositing a slurry of 4.4% A1 0 and 95.6% MgCr O (calcinedcoprccipitated at 600 C. .for 2 hours in air) on to HCl Mole percent 60S 74 12 44 No substantial advantage was obtained from adding anadditional Al (SO -18H O to the calcined catalyst.

leached alumina and drying the catalyst. 4.4% A1 0 corresponds to 20% Al(SO -16H O. The A1 0 was approximately 90% gamma alumina (Alon fumedalumina). The dehydrogenation was carried out at 1 atmosphere using puren-butane at LHSV of 1 at 600 C. for about 24 hours using the 9/9 minutecycle. The results were =0.33 atm.=hcbn plus Ni.

but substantial Results C Bu Bd Bu Bd 0.022 mole or Alz(SO4)a.18H2O.

19 Coprec. of Cr/Mg=2/1 calcined to 800 0.; 42.5 gms. of calcinedproduct plus 0.022 mole of Al2(SO4)a.18HzO.

X Supported on 7-9 mesh AMC alumina. 2 Pp of n-C4=1.0 atrm.=pure hcbnfeed; pp of 11-04 The noticeable trends with increasing calcinationtemperature are the decrease in conversion increase in selectivities.

Examples 20 and 21 These examples are presented to show the combination35 of Al in a chromite of the formula MgAl Cr Table IV sets forth theconcition and results.

TABLE IV Conditions;

LHsv=1.0, Tm=-600 0. Reaction cycle=9 minutes reaction/9 minutesregeneration Feed=99 mole percent butane Hours on stream524 Example 23This series of runs was made to demonstrate the catalyst with an excessof either Mg or Cr over the stoichiometric amount. The variation wasobtained by using the portion of soluble salts to give the Mg:Cr atomratios shown in Table V. The improvement for each ratio with added Al isalso shown in Table V along with the conditions. =1.0, atmosphericConditions:

LHSV Reaction cy Feed= 1 6-8 mesh particles of wt. percent activesdeposited on 7-9 mesh, HCl leached AMC alumina support.

2 Pp ofn-C4=1.0 atm. =pure hcbn feed: pp of nC4=0.33 atm.=hcbn plus N adiluent.

x in Mg ch04 aeeeama nmamwaa commune aaaamen 4 Jeanin Isothermal vacuumreactor (Examples 24-47) The reactor was an alonized 316 SS tube, 24inches long and 1 inch in diameter equipped with a heating mantel andthermoelectric temperature controller. A 160 cc. bed of catalyst mixedwith 48 cc. of fused alumina balls) was used for each run. The reactantfeed was passed down through the catalyst bed and the products removedat the bottom. The catalyst was heated to reaction temperature TAB LE VIConditions: LHSV=1.25, Tm=-550 0. (1,022 F.) Pressure=22" Hg vacuum 9min. reaction 9 min. regeneration Reaction cycle=590 cc./mln. of 1 min.N 1,500 cc./m.in. of artificial n-C; purge air=300 cc./min. 01 plusFeed=99 mole percent n'butane 1,200 cc./min. N,

Results, mole percent 8 Y Total hrs.

Example Catalyst on stream C Bu Bd Bu Bd 24 f52"d18.MgC1'104 (eoprec.ofCr/Mg=2/1 calcinedto 600 C.).- 90.5 22.4 70.8 10.6 15.8 2.4 138.5 21.168.4 11.2 14.4 2.4

25 55:dla. pellets of MgCr104 (coprec. oi CrlMg=2l1 calcined to 21.550.2 77.0 6.9 38.6 3.5 600 0.) plus 26wt. percent Alz(S0):-18Hg0. 44.561.0 72.1 I 7.9 44.0 4.8

26 Non-calcined co rec. of Cr/Mg=2/1 plus appropriate amount 115.0 44.574.3 10.5 33.1 4.7 oiAl (S04)a-18 208DdthBIDiXtUIBOSIC1DBdtO6QOC-8I1d161.0 44.9 76.0 10.3 34.1 4.6

formed into %zdia.MgCr04 pellets. 234.0 40.4 76.5 10.1 30.9 4.1

27 54:" dia. pellets MgCrzOr coprec. of CrIMg=2l1 calcined to 95.0 67.863.7 7.1 43.2 4.8 600C. plusBSwt. percentAl(NO;);-9HzO. 190.5 64.5 66.68.4 42.9 5.4

1 Flow of O: was increased from 300 cc./mln. to 345 ccJmin. to effectcomplete regeneration.

in a nitrogen atmosphere. The process was carried out in 45 cycles of 9minutes of reaction, 1 minute of nitrogen purge, 9 minutes ofregeneration, followed by reaction, etc. A vacuum of 22 inches of Hg wasmaintained during the reaction cycle and atmospheric pressure usedduring Examples 28, 29 and 30 These examples show a range of aluminumconcentration in the catalyst. Table VII shows the conditions andresults.

TABLE VII Conditions: LHSV=L25 Pressure=22" Hg vacuum 9 min. reaction 9min. regeneration Reaction cycle= 590 ccJmln. 1 min. N: 1,500 cc./mln.oi artificial of n-Cr purge alr=300 cc.lmin. 0 plus Feed= 99 molepercent n-buatne 1,200 ceJmin. N1

Results, mole percent Total 8 Y hrs. on Tm, Example Catalyst stream C. CBu Bd Bu Bd 28 94: dia. pellets of MgCr2O4 (coprec. of CrlMg=2l1calcined to 700 C.) 23.0 550 56.8 71.5 9.2 40.6 5. plus 15 wt. percentA1 (80 -16 H90. 94. 5 550 59.4 70. 5 9.3 41.9 5. 117. 5 550 60. 2 69. 19. 6 41. 6 5. 3 141. 5 550 60. 0 70. 3 9. 8 42. 2 5. 9 165.5 525 50.578.6 7.9 89.7 4.0 189.5 525 52.1 79.1 7.3 41.2 3.8

29 62" dia. pellets of MgCIzO4 (coprec. oi Cr/Mg=2/1 calcined to 700 C.)69.5 550 56.0 72.2 9.0 40.5 5.1 plus 20 wt. percent Alz(SO1)3-16 H 0.97. 5 550 57. 7 73.1 8. 6 42.2 4. 9 117.5 550 59. 2 75. 1 8. 8 44. 5 5.2 165.5 550 59.0 73.2 8.9 43.1 5.2 238.0 550 59.4 73.0 9.8 43.4 5. 8

30 552" die. pellets of MgCrzO; (coprec. of OrIMg=2l1 calcined to 700C.) 67.0 550 59.3 71.2 11.0 42.2 6.5 plus 25 wt. percent A12(SO4)a-16H20. 90. 5 550 59. 7 71. 1 10. 9 42.4 6. 5 186.0 550 60.1 71.8 10.3 43.16.2 321.0 525 48.2 81.5 7.8 39.3 3 7 dehydrogenation and regeneratingsaid catalyst by contacting said catalyst with molecular oxygen whereinthe improvement comprises employing a dehydrogenation catalyst having anactive surface available for contact with the gaseous reactants the saidactive surface comprising predominantely magnesium chromite and apromoting amount of aluminum contained therein or intimately admixedtherewith the said active surface having in contact with the gaseousreactants aluminum and chromium in an AlzC'r ratio of from .0004 to12:1.

2. The process according to claim 1 wherein the hydrocarbon has 3 tocarbon atoms.

3. The process according to claim 2 wherein the atomic ratio of AlzCr is0.04 to 0.8:1.

4. The process according to claim 3 wherein the aluminum is present in acompound of the formula MeA1 Cr- O where Me is Mg or Mg and one or moreof the divalent ions of Ca, Sr, Ba, Fe, Mn, Co, Ni, Cu, Zn or Cd,provided that Mg comprises at least 50 atomic percent of said Me ionsand x is a number of from more than 0 up to less than 1.

5. The process according to claim 3 wherein the aluminum is present asaluminum oxide.

6. The process according to claim 1 wherein aluminum oxide is present.

References Cited UNITED STATES PATENTS 3,433,851 3/1969 Keblys 260-683.32,419,997 5/ 1947 Houndry 260-683.3 2,399,678 5/1946 Houndry 260-683.32,664,451 12/ 1953 Owen 260-683.3 2,122,787 7/1938 Tropsch 260-2,122,786 7/1938 Tropsch 260-170 2,122,790 7/ 1938 TrOpsCh 260-170DELBERT E. GANTZ, Primary Examiner I. M. NELSON, Assistant Examiner U.S.Cl. X.R. 260-680 R UNiTED STATES PATENT OFFICE GERTIFICATE OF CORRECTIONme e 1% 3, 781, 376 I Dated December25, 1973 inventnfla) Harold E.Manning It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown belowCol. 6, line 34 reads "distribtuion" but should read"- distribution Col.8, lines approx. 681 7, Table I reading across from Example 4 undercolumn headed Bd (second occurrence) reads 6 but should read 6 4 Col 8,lines approx. 9, Table 1 reading across from Example 5 under columnheaded Bd (second occurrence) reads "48" but should read 8 Table II,2nd, line reads "LSHV" but should read LHSV Col. 9, line 40 reads"Conditions;" but should read Conditions: Table V, 3rd line under Bu(first occurrence) reads "69+" but should read 68+ Col. 11, line 4 reads"catalyst mixed" but should read catalyst (112 cc of catalyst mixedTableVIl, third item reads Feed 99 mole percent n-buatne" but shouldread Feed 99 mole percent n-butane Table VIII, third item reads "Feed 99mole percent n-buatne" but should read Feed: 99 mole n-butane TableVIII, heading for right column reads "Pressure= 22 Hg vacuum" but shouldread Pressure 22" Hg vacuum Table 1X, 2nd, col. Example 37 reads "HoukryC+".but should read Houdry C+ Table IX, 2nd. col. Example 4 reads "(6. 7wt. Al (SO). but should read (6. 7 wt. %)Al (SO I Col. 15, line 6 reads"predominantely" but should read predominately Col 5, line 9 reads"250-252" but should read 2.50 252 Signed and sealed this 15th day ofJuly 1975.

(SEAL) Attest:

C. MARSHALL DANN RUTH C. MASON Commissioner of Patents Attesting Officerand Trademarks

